Up that 4 to 5.Please Register or Log in to view the hidden image! I have been patient trying to see where you were going. Almost jumped a while back to ask if you really wanted / expected some one to prove anything existed, if all they could use in their proof was a vast nothingness, completely free of all matter, but did not. I am posting now as it seems to me to very simple to separate the “EM” and the “reflector.” I think it safe to assume that the interaction between the reflector and EM is local. Thus fact that it take longer for light reflected by a reflector left on the moon to return to Earth based laser source than if the reflector on the other wall over there, must not be attributed to the reflector alone. I.e. there must be something else. I.e. there is something traveling. I don't care too much what it is called, but as I do have a conventional streak, I prefer "photon" for name of this carrier of energy. Also in spite of your not wanting to use interactions with matter, I can not help but be impressed by how well the measured energy it dose carry correlates with the angles and the grading equation's predictions of them when a spectral grading reflection takes place. (Spectrograph). Thus, I think these photons have both “energy” and a "wavelength" with an inversely proportionality between these two properties that all photons demonstrate.